Electrooptical liquid crystal display

ABSTRACT

The invention relates to an electrooptical liquid crystal display comprising a reorientation layer for reorientation of the liquid crystals. The field of said reorientation layer has a component parallel to the liquid crystal layer, said component being crucial for the reorientation. Said component comprises a liquid-crystalline medium having a positive dielectric anisotropy and contains at least one mesogenic compound of the formula (I), wherein R 1  and L are delined as in claim 1.

The invention relates to an electro-optical liquid-crystal displayhaving a realignment layer for realignment of the liquid crystals whosefield has a component parallel to the liquid-crystal layer that iscrucial for the realignment, containing a liquid-crystalline medium ofpositive dielectric anisotropy, where the medium comprises at least onemesogenic compound of the formula I.

In conventional liquid-crystal displays (TN, STN, OMI or AMD-TN), theelectric fields for realignment are generated essentially perpendicularto the liquid-crystal layer.

International Patent Application WO 91/10936 discloses a liquid-crystaldisplay in which the electric signals are generated in such a way thatthe electric fields have a significant component parallel to theliquid-crystal layer (IPS, in-plane switching). The principles ofoperating a display of this type are described, for example, by R. A.Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468(1974).

EP 0 588 568, for example, discloses various possibilities for thedesign of the electrodes and for addressing a display of this type. DE198 24 137 likewise describes various embodiments of IPS displays ofthis type.

Liquid-crystalline materials for IPS displays of this type aredescribed, for example, in DE 195 28 104.

The IPS displays containing the known liquid-crystalline media arecharacterised by inadequate, long response times and often excessivelyhigh operating voltages. There is thus a demand for IPS displays whichdo not have these disadvantages or only do so to a reduced extent. Tothis end, in particular liquid-crystalline materials are required which,besides an adequate phase range, low tendency towards crystallisation atlow temperatures, low birefringence and adequate electrical resistance,have, in particular, low threshold voltages (V₁₀) and low rotationalviscosities (γ₁), which are crucial for the response times.

This object has, surprisingly, been achieved by the use ofliquid-crystalline materials in mixtures which comprise at least onecompound of the formula I.

The IPS mixtures according to the invention are distinguished by theirrelatively low rotational viscosity values γ₁ and their low thresholdvoltage and response time values.

The invention thus relates to an electro-optical liquid-crystal having arealignment layer for realignment of the liquid crystals whose field hasa significant component parallel to the liquid-crystal layer, containinga liquid-crystalline medium of positive dielectric anisotropy, where themedium comprises at least one compound of the formula I

in which

R¹ is an alkyl or alkenyl radical having up to 15 carbon atoms which isunsubstituted, monosubstituted by CN or CF₃ or at least monosubstitutedby halogen and in which, in addition, one or more CH₂ groups in theseradicals may each, independently of one an other, be replaced by —O—,—S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, and

L is H or F.

Particular preference is given to compounds of the formula I in which Lis F.

In the compounds of the formula I, R¹ is preferably alkyl or alkenylhaving up to 7 carbon atoms. R¹ is preferably ethyl, n-propyl, n-pentyl,vinyl, 1E-alkenyl or 3E-alkenyl.

The compounds of the formula I have high dielectric anisotropy valuesand relatively high birefringence and clearing point values. Their usein liquid-crystal mixtures for IPS displays according to the inventionfacilitates high dielectric anisotropies and low rotational viscositieswith retention of high clearing points and favourable birefringencevalues and effects low threshold voltages and short response times.

It has been found, in particular, that IPS mixtures according to theinvention comprising one or more, preferably one or two, compounds ofthe formula I have significantly higher dielectric anisotropy values,lower rotational viscosity and threshold voltage values, as well asshorter response times than, for example, analogous mixtures which,instead of the compounds of the formula I, comprise3,5-difluoro-4-cyanophenylcyclohexanes of the formula

Some of the compounds of the formula I are disclosed in DE 40 27 869 A1.However, this patent application does not describe IPS displays.

Preferred embodiments are IPS displays in which

a) the liquid-crystalline medium additionally comprises one or morecompounds of the formula II containing a cyano group

 in which

R² is H, an alkyl or alkenyl radical having up to 15 carbon atoms whichis unsubstituted, monosubstituted by CN or CF₃ or at leastmono-substituted by halogen and in which,,in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another,

A¹ and A² are each, independently of one another,

(a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenylene radical, inwhich, in addition, one more non-adjacent CH₂ groups may be replaced by—O— and/or —S—,

(b) a 1,4-phenylene radical, in which, in addition, one or two CH groupsmay be replaced by N,

(c) a radical from the group consisting of 1,4 bicyclo[2.2.2]octylene,piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyland 1,2,3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals (a), (b) and (c) may be substituted by one or twofluorine atoms,

Z¹ and Z² are each, independently of one another, —CO—O—, —O—CO—,—CH₂O—, —OCH₂—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—,—OCF₂—, —CF₂CF₂— or a single bond, and one or the radicals Z¹ and Z² isalternatively —(CH₂)₄— or —CH═CH—CH₂CH₂—,

L¹ and L² are each, independently of one another, H or F, and

m is 0, 1 or 2,

b) the liquid-crystalline medium comprises one or more compounds of theformula III containing a 3,4,5-trifluorophenyl group

 in which

R³ has one of the meanings indicated for R² in the formula II,

A³ and A⁴ each, independently of one another, have one of the meaningsindicated for A¹ and A² in the formula II,

Z³ and Z⁴ each, independently of one another, have one of the meaningsindicated for Z¹ and Z² in the formula II, and

n is 0, 1or 2,

c) the liquid-crystalline medium comprises one or more compounds of theformula IV

R⁴-(A⁵-Z⁵)_(o)-A⁸-R⁵  IV

in which

R⁴ and R⁵ each, independently of one another, have one of the meaningsindicated for R² in the formula II,

A⁵ and A⁶ each, independently of one another, have one of the meaningsindicated for A¹ and A² in the formula II,

each Z⁵, independently of the others, has one of the meanings indicatedfor Z¹ and Z² in the formula II, and

o is 1, 2 or 3

d) the liquid-crystalline medium additionally comprises one or morecompounds of the formula V

 in which

R⁶ has one of the meanings indicated for R² in the formula II,

A⁷ and A⁸ each, independently of one another, have one of the meaningsindicated for A¹ and A² in the formula II,

Z⁷ and Z⁸ each, independently of one another, have one of the meanings:indicated for Z¹ and Z² in the formula II,

L¹ and L² are each, independently of one another, H or F,

Q is a polyfluoroalkylene radical of the formula:

—(O)_(q)—(CH₂)_(r)—(CF₂)_(s)—,—(O)_(q)—(CHF)_(r)—(CF₂)_(s)— or

—(O)_(q)—(CF₂)_(r)—(CHF)_(s)—CF₂—, in which

q is 0 or 1,

r is 0, 1, 2, 3, 4, 5 or 6,

s is 1, 2, 3, 4, 5 or 6,

X is H, F or Cl, and

p is 0, 1 or 2, and/or

e) the liquid-crystalline medium additionally comprises one or morecompounds of the formula III′

 in which

R^(3′) has one of the meanings indicated for R² in the formula II,

A^(3′) and A^(4′) each, independently of one another, have one of themeanings indicated for A¹ and A² in the formula II,

Z^(3′) and Z^(4′) each, independently of one another, have one of themeanings indicated for Z¹ and Z²in the formula II, and

n′ is 0, or 2.

The compounds of the formula II are preferably selected from the groupcomprising the formulae IIa to IIq:

in which R² is as defined in the formula II, and L¹ and/or L² is H or F.

In the compounds of the formulae IIb, IIe, IIk, IIn and IIp, L² isparticularly preferably F. In the compounds of the formulae IId, IIg,IIh and IIi, L² is particularly preferably H. In the compounds of theformula IIo and/or IIp, L¹ and L² are preferably fluorine.

The liquid-crystalline medium particularly preferably comprises one ormore compounds selected from the group consisting of the compounds ofthe formulae IIa, IIb, IIc, IId, IIh, IIk and IIp.

In a further preferred embodiment, the liquid-crystalline mediumcomprises at least one heterocyclic compound selected from the groupcomprising the formulae IIm, IIn, IIo and IIp.

The compounds of the formula III are preferably selected from the groupcomprising the formulae IIa to IIIp and III″a,

in which R³ is as defined in the formula III.

The liquid-crystal display particularly preferably contains aliquid-crystalline medium comprising one or more compounds selected fromthe group comprising the formulae IIIc, IIId, IIIe, IIIf, IIIg, IIIh,IIIi, IIIk and IIIn.

The compounds of the formula III′ are preferably selected from the groupcomprising the formulae III′a to III′l:

in which

R^(3′) is as defined above under the formula III′.

As an alternative to or in addition to one or more compound(s) of theformula IIIc, the liquid-crystalline medium may comprise one or morecompounds of the formula III′a,

in which R^(3′) is as defined above under the formula III′.

The compounds of the formula IV are preferably selected from the groupcomprising the formulae IVa to IVn:

in which R⁴ and R⁵ are as defined in the formula IV, and L is H or F.

In the compounds of the formula IVj, L is particularly preferably F.

The liquid-crystal display particularly preferably contains aliquid-crystalline medium comprising one or more compounds selected fromthe group consisting of the compounds of the formulae IVb, IVe, IVk andIVm.

The compounds of the formula V are preferably selected from the groupcomprising the formulae Va to Vm:

in which R⁶ is as defined in the formula V, and L² is H or F.

In the compounds of the formula Vd, L² is particularly preferably F.

The liquid-crystalline medium particularly preferably comprises one ormore compounds selected from the group consisting of the compounds ofthe formulae Va, Vc, Vd, Ve and Vf.

In a preferred embodiment, the liquid-crystalline medium comprises oneor two compounds of the formula I and one or two compounds of theformula Ve.

In a further preferred embodiment, the liquid-crystalline mediumcomprises one or more alkenyl compounds of the formula VI

in which

R⁷ is an alkenyl group having 2 to 7 carbon atoms,

Z⁹ is —CH═CH—, —CH₂CH₂- or a single bond,

L is H or,F,

a is 0 or 1 and

R⁸ is an alkyl, alkoxy or alkenyl group having up to 12 carbon atoms, inwhich, in addition, one or two non-adjacent CH₂ groups may be replacedby —CO—, —OCO— or —COO—, or, if a is 1, R⁸ may alternatively be F.

The compounds of the formula VI are preferably selected from the groupcomprising the formulae VIa to VIf:

in which

k is 1, 2, 3, 4 or 5,

y and z are each, independently of one another, 0, 1, 2 or 3, where y+zis <≦5, and

x is 0 or 1.

In the compounds of the formula VIf, L is preferably F.

The mixtures according to the invention preferably comprise one or twocompounds of the formula IVb and one or two compounds of the formulaVIa.

Further preferred embodiments are the following mixtures for IPSdisplays:

The medium additionally comprises one or more compounds containing a4-fluoro-phenyl group, selected from the group consisting of theformulae VIIa to VIIc:

 in which R⁹ has the one of the meanings indicated for R³ in the formulaIII, and in particular is alkyl having 1 to 7 carbon atoms;

The medium additionally comprises one or more compounds of the formulaVIII

 in which R¹⁰ and R¹¹ are each, independently of one another,straight-chain alkyl or alkoxy; preferably alkyl, having 1 to 7 carbonatoms;

The medium additionally comprises one or more compounds of the formulaIX

 in which R¹² has one of the meanings indicated for R¹.

The medium additionally comprises one or more compounds of negativedielectric anisotropy selected from the group consisting of the formulaeX, XI and XII:

 in which R¹³ and R¹⁴ each, independently of one another, have one ofthe meanings indicated for R¹, and b is 0 or 1. R¹³ and R¹⁴ arepreferably straight-chain alkyl or alkoxy having 1 to 7 carbon atoms,furthermore alkenyl or alkenyloxy having up to 7 carbon atoms. Inparticular, R¹³ is preferably alkyl and R¹⁴ is preferably alkoxy.

The medium additionally comprises one or more difluorostilbenes of theformula XIII,

 in which

Alkyl* and Alkyl** are a straight-chain alkyl radical having 1 to 6carbon atoms, preferably 2 to 5 carbon atoms.

The % proportion of the difluorostilbenes in the mixture according tothe invention is from 0 to 30% by weight, preferably from 0 to 20% byweight, in particular from 0 to 15% by weight.

The medium additionally comprises one or more compounds of the formulaXIV

in which

R¹⁵ is as defined for R¹ , and

L¹ and L² are each, independently of one another, H or F.

The proportion of the compounds of the formula XIV in the mixtureaccording to the invention is from 0 to 30% by weight, preferably from 0to 20% by weight, in particular from 0 to 15% by weight.

The medium additionally comprises one or more compounds of the formulaXV

in which

R¹⁶ is as defined for R¹, preferably is straight-chain alkyl or alkoxyhaving 1 to 3 carbon atoms.

The % proportion of the biphenyls in the mixture according to theinvention is from 0 to 30% by weight, preferably from 0 to 20% byweight, in particular from 0 to 15% by weight.

Preference is given to displays containing liquid-crystal mixturescomprising

one or more cyano compounds selected from the group comprising theformulae IIa, IIb, IId, IIg and IIk, in particular compounds of theformulae IIb, IIg and IIk in which L² is F, and compounds of the formulaIII in which L² is H,

one or more dioxane compounds selected from the group comprising theformulae IIk and III, in particular of the formula III in which L² s F,

one or more 3,4,5-trifluorophenyl compounds selected from the groupcomprising the formulae IIIc, IIIf, IIIg and IIIh,

one or more compounds selected from the group comprising the formulaeIVb, IVh, IVk and IVm. R⁴ and R⁵ are preferably straight-chain alkylhaving 1 to 7 carbon atoms.

In the compounds of the formula IVb, R⁵ is preferably alkoxy having 1 to5 carbon atoms. In the compounds of the formula IVj, L is preferably F,

one or more compounds selected from the group comprising the formulaeVa, Vb, Vd and Ve,

one or more alkenyl compounds selected from the group comprising theformulae VIa, VIb, VIe and VIf,

in the compounds of the formula VIa, y and z are particularly preferably0 or 1,

in the compounds of the formula VIb, z is preferably 0,

in the compounds of the formula VIe, k is preferably 0,

in the compounds of the formula VIf, L is preferably F, and y and z arepreferably 0.

Preference is furthermore given to a liquid-crystal display according tothe invention in which the pixels are addressed by means of an activematrix.

The invention furthermore relates to a liquid-crystalline medium ofpositive dielectric an isotropy comprising at least one compound of theformula 1, at least one compound selected from the group consisting ofthe compounds of the formulae IIa to IIp, IIIa to IIIo and Va to Vk, atleast one compound selected from the group consisting of the compoundsof the formulae VIa to VIf, and, if desired, one or more compoundsselected from the group consisting of the compounds of the formulae IVato Ivn.

Particular preference is given to mixtures which comprise

from 2 to 40% by weight, preferably from 3 to 30% by weight,particularly preferably from 3 to 25% by weight, of at least onecompound of the formula I, from 15 to 85% by weight, preferably from 20to 65% by weight, of at least one compound selected from the groupconsisting of the compounds of the formulae II and III, from 0 to 60% byweight, preferably from 5 to 45% by weight, of at least one compound ofthe formula IV, from 0 to 40% by weight, preferably from 5 to 35% byweight, particu- larly preferably from 10 to 25% by weight, of at leastone compound of the formula V, from 0 to 55% by weight, preferably from5 to 45% by weight, of at least one compound of the formula VI.

The liquid-crystalline media used in accordance with the inventiongenerally have a birefringence (Δn) of <0.14, preferably in the rangefrom 0.06 to 0.13, in particular in the range from 0.09 to 0.12; withclearing points of from 60 to 95° C., in particular from 65 to 85° C.

The flow viscosity ν₂₀ (at 20° C.) of the mixtures used in accordancewith the invention is generally less than 30 mm²·s⁻¹, in particularbetween 15 and 25 mm²·s⁻¹. The specific resistance of the materialsaccording to the invention is generally, at 20° C., from 5×10¹⁰ to5×10¹⁴ Ω·cm, the values are particularly preferably from 5×10¹¹ to5×10¹³ Ω·cm. The rotational viscosity γ₁ of the mixtures according tothe invention is, at 20° C., preferably less than 80 mPa·s, inparticular less than 65 mPa·s.

The clearing point of the media used in accordance with the invention isgreater than 60° C., preferably greater than 65° C. and particularlypreferably 70° C. or greater. In particular, the clearing point is inthe range from 60° C. to 85° C.

The shelf life in test cells, determined as described below, is 1000hours or more at −30° C., preferably 500 hours or more at −40° C. andvery particularly preferably 1000 hours or more at −40° C.

The media used in accordance with the invention consist of from 5 to 30compounds, preferably of from 6 to 20 compounds and particularlypreferably of from 7 to 16 compounds. The mixtures according to theinvention preferably comprise one or two compounds of the formula I.

It has been found that even a relatively low proportion of compounds ofthe formula I in a mixture with conventional liquid-crystal materials,but in particular with one or more compounds selected from the groupconsisting of the compounds of the formulae IIa to IIp and/or from thegroup consisting of the compounds of the formulae IVa to IVn, results ina significant lowering of the threshold voltage, in very low rotationalviscosity values γ₁ and in fast response times, with, in particular,broad nematic phases with low smectic-nematic transition temperaturesbeing observed. The compounds of the formulae I to VI are colourless,stable and readily miscible with one another and with otherliquid-crystal materials.

The term “alkyl” covers straight-chain and branched alkyl groups having1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl,propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbon atomsare preferred.

The term “alkenyl” covers straight-chain and branched alkenyl groupshaving 2-7 carbon atoms, in particular the straight-chain groups.Particularly preferred alkenyl groups are C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, and C₆-C₇₋5-alkenyl and C₇-6-alkenyl,in particular C₂-C₇-1 E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples of very particularly preferred alkenyl groups are vinyl,1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl,3E-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl,4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like.Groups having up to 5 carbon atoms are preferred.

The term “fluoroalkyl” preferably covers straight-chain groups having aterminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl,4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl.However, other positions of the fluorine are not excluded.

The term “alkoxyalkyl” preferably covers straight-chain radical s of theformula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and m are each,independently of one another, from 1 to 6. Preferably, m=1 and n is from1 to 4.

Through a suitable choice of the meanings of R¹ to R¹⁴, the addressingtimes, the threshold voltage, the steepness of the transmissioncharacteristic lines, etc., can be modified in the desired manner. Forexample, 1E-alkenyl radicals, 3E-alkenyl radicals 2E-alkenyloxy radicalsand the like generally result in shorter addressing times, improvednematic tendencies and a higher ratio of the elastic constants k₃₃(bend) and k₁₁ (splay) compared with alkyl and alkoxy radicals.4-alkenyl radicals, 3-alkenyl radicals and the like generally give lowerthreshold voltages and smaller values of k₃₃/k₁₁ compared with alkyl andalkoxy radicals.

The optimum mixing ratio of the compounds of the formulae I-VI dependssubstantially on the desired properties, on the choice of the componentsof the formulae I, II, III, IV, V and/or VI and on the choice of anyfurther components present. Suitable mixing ratios within the rangeindicated above can easily be determined from case to case.

The total amount of compounds of the formulae I to VI in the mixturesaccording to the invention is not crucial. The mixtures preferably chainof 50-90% a weight of compounds of the formulae I to VI. The mixturesmay also comprise one or more further components in order to optimisevarious properties. However, the observed effect, particularly on thelow-temperature stability, is generally greater the higher the totalconcentration of compounds of the formulae I to VI.

The liquid-crystalline media according to the invention preferablycomprise from 2 to 40, in particular from 4 to 30, compounds as furtherconstituents besides one or more compounds of the formula I. These mediavery particularly preferably comprise from 7 to 25 compounds besides oneor more compounds of the formula I. These further constituents arepreferably selected from nematic or nematogenic (monotropic orisotropic) substances, in particular substances from the classes of theazoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl orcyclohexyl benzoates, phenyl or cyclohexyl esters ofcyclohexane-carboxylic acid, phenyl or cyclohexyl esters ofcyclohexylbenzoic acid, phenyl or cyclohexyl esters ofcyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoicacid, of, cyclohexanecarboxylic acid or ofcyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexyl-cyclohexylcyclohexenes,1,4-bis-cyclohexylbenzenes, 4,4′-bis-cyclohexylbiphenyls, phenyl- orcyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- orcyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes,1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundsmay also be fluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterised by the formulae 1, 2, 3,4 and 5:

R′—L—E—R″ 1 R′—L—COO—E—R″ 2 R′—L—OOC—E—R″ 3 R′—L—CH₂CH₂—E—R″ 4R′—L—C≡C—E—R″ 5

In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical ordifferent, are each, independently of one another, a bivalent radicalfrom the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-,-Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe isunsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr is pyrimidine-2,5-diyl orpyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl, and G is2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr, E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably comprise one or more components selected from the compoundsof the formulae 1, 2, 3, 4 and 5 in which L and E are selected from thegroup consisting of Cyc, Phe and Pyr and simultaneously one or morecomponents selected from the compounds of the formulae 1, 2, 3, 4 and 5in which one of the radicals L and E is selected from the groupconsisting of Cyc, Phe and Pyr and the other radical is selected fromthe group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and-G-Cyc-, and optionally one or more components selected from thecompounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and Eare selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe-and -G-Cyc-.

In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and5, R′ and R″ are each, independently of one another, alkyl, alkenyl,alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbonatoms. This smaller sub-group is called group A below, and the compoundsare referred to by the sub-formulae 1 a, 2a, 3a, 4a and 5a. In most ofthese compounds, R′ and R″ are different from one another, one of theseradicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4and 5, which is known as group B, R″ is —F, —Cl, —NCS or—(O)_(i)CH_(3−(k+l))F_(k)Cl_(I), where i is 0 or 1, and k+l is 1, 2 or3; the compounds in which R″ has this meaning are referred to by thesub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given tothose compounds of the sub-formulae 1 b, 2b, 3b, 4b and 5b in which R″is —F, —Cl, —NCS, —CF₃, SF₅, —OCHF₂ or —OCF₃.

In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, R′ is asdefined for the compounds of the sub-formulae 1a-5a and is preferablyalkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller sub-group of the compounds of the formulae 1, 2, 3,4 and 5, R″ is —CN; this sub-group is referred to below as group C, andthe compounds of this sub-group are correspondingly described bysub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae1 c, 2c, 3c, 4c and 5c, R′ is as defined for the compounds of thesub-formulae 1 a-5a and is preferably alkyl, alkoxy or alkenyl.

Besides the preferred compounds of groups A, B and C, other compounds ofthe formulae 1, 2, 3, 4 and 5 having other variants of the proposedsubstituents are also customary. All these substances are obtainable bymethods which are known from the literature or analogously thereto.

Besides the compounds of the formula I to VI, the media according to theinvention preferably comprise one or more compounds selected from groupA and/or group B and/or group C. The proportions by weight of thecompounds from these groups in the media according to the invention arepreferably

group A: from 0 to 90%, preferably from 20 to 90%, in particular from 30to 90% group B: from 0 to 80%, preferably from 10 to 80%, in particularfrom 10 to 65% group C: from 0 to 80%, preferably from 5 to 80%, inparticular from 5 to 50%,

the sum of the proportions by weight of the group A and/or B and/or Ccompounds present in the respective media according to the inventionpreferably being from 5% to 90% and in particular from 10% to 90%.

The structure of the IPS display according to the invention correspondsto the usual design for displays of this type, as described, forexample, in WO 91/10936 or EP 0 588 568. The term usual design isbroadly drawn here and also covers all derivatives and modifications ofthe IPS display, in particular, for example, also matrix displayelements based on poly-Si TFT or MIM.

However, an essential difference of the displays according to theinvention from those usual hitherto consists in the choice of theliquid-crystal parameters of the liquid-crystal layer.

The liquid-crystal mixtures which can be used in accordance with theinvention are prepared in a manner conventional per se. In general, thedesired amount of the components used in smaller amount is dissolved inthe components making up the principal constituent, advantageously atelevated temperature. It is also possible to prepare the mixtures inother conventional manners, for example by use of pre-mixtures, forexample homologue mixtures, or using so-called “multibottle” systems .

The dielectrics may also comprise further additives known to the personskilled in the art for described in the literature. For example, 0-15%preferably 0-10%, of pleochroic dyes and/or chiral dopants may be added.The individual compounds added are employed in concentrations of from0.01 to 6% and preferably from 0.1 to 3%. However, the concentrationsgiven here for the other constituents of the liquid-crystal mixtures,i.e. the liquid-crystalline or mesogenic compounds, are indicatedwithout taking into account the concentration of these additives.

The physical properties of the liquid-crystal mixtures are determined inaccordance with “Physical Properties of Liquid Crystals” Ed. W. Becker,Merck KGaA, as of Nov. 1997, unless explicitly stated otherwise.

C denotes a crystalline phase, S a smectic phase, S_(C) a smectic Cphase, S_(A) a smectic A phase, N a nematic phase and I the isotropicphase.

V₀ denotes the capacitive threshold voltage. Δn denotes the opticalanisotropy, and n₀ the ordinary refractive index (in each case at 589nm). Δ∈ denotes the dielectric anisotropy (Δ∈=∈_(∥)−∈_(⊥), where ∈_(∥)denotes the dielectric constant parallel to the longitudinal molecularaxes and ∈_(⊥) denotes the dielectric constant perpendicular thereto, ineach case at 1 kHz). The electro-optical data were measured in a planarcell at 20° C., unless expressly stated otherwise. All physicalproperties are indicated and measured at 20° C., unless expressly statedotherwise.

The cells are preferably bright in the “off” state.

The examples below are intended to illustrate the invention withoutrepresenting a limitation. Above and below, percentages are per cent byweight. All temperatures are indicated in degrees Celsius. Δn denotesoptical anisotropy (589 nm, 20° C), Δ∈ denotes the dielectric anisotropy(1 kHz, 20° C.), H.R. denotes the voltage holding ratio (at 100° C.,after 5 minutes in an oven at 1 V). The capacitive threshold voltage V₀was determined at 20° C. and 1 kHz.

The calibrated rotational viscometer gave a rotational viscosity γ₁ forZLI-4792 (Merck KGaA) of 133 mPa·s at 20° C.

The shelf life was investigated in sealed test cells with an opticalretardation of about 0.5 μm with CU-1511 from DuPont, USA, as alignmentlayer. To this end, in each case five test cells were bonded on bothsides to crossed polarisers and stored at fixed temperatures of 0° C.,−10° C., −20° C., −30° C. and −40° C. At intervals of 24 hours in eachcase, the cells were assessed visually for changes. The storage timenoted at the respective temperature t_(store) (T) was the final time atwhich a change was just not observed in any cell.

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by means of acronyms, thetransformation into chemical formulae taking place in accordance withTables A and B below. All radicals C_(n)H_(2n+1) and C_(m)H_(2m+1) arestraight-chain alkyl radicals having n, respectively m, carbon atoms.The coding in Table B is self-evident. In Table A, only the acronym forthe parent structure is indicated, followed in individual cases,separated from the acronym for the parent structure by a dash, by a codefor the substituents R¹, R², L¹ and L²:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H HnOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) HH n C_(n)H_(2n+1) CN H H nN.F C_(n)H_(2n+1) CN F H nN.F.F C_(n)H_(2n+1)CN F F nF C_(n)H_(2n+1) F H H nOF OC_(n)H_(2n+1) F H H nCl C_(n)H_(2n+1)Cl H H nF.F C_(n)H_(2n+1) F F H nCF₃ C_(n)H_(2n+1) CF₃ H H nOCF₃C_(n)H_(2n+1) OCF₃ H H nOCF₂ C_(n)H_(2n+1) OCHF₂ H H nS C_(n)H_(2n+1)NCS H H rVsN C_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H rEsNC_(r)H_(2r+1)—O—C₅H_(2s)— CN H H nAm C_(n)H_(2n+1) C≡C—C_(m)H_(2m+1) H HnF.F.F C_(n)H_(2n+1) F F F nCl.F.F C_(n)H_(2n+1) Cl F F nCF₃.F.FC_(n)H_(2n+1) CF₃ F F nOCF₃.F.F C_(n)H_(2n+1) OCF₃ F F nOCF₂.F.FC_(n)H_(2n+1) OCHF₂ F F nOCF₃.F C_(n)H_(2n+1) OCF₃ F H

Preferred displays contain media comprising one or more compounds fromTables A and B in addition to one or more compounds of the formula I.

TABLE A

TABLE B

TABLE C Table C shows dopants which are usually employed in the mixturesaccording to the invention

EXAMPLE 1

An IPS display contains a nematic mixture having CC-3-V  19.0% CC-3-V1 9.0% CCH-35  5.0% PDX-3  5.0% ME2N.F  4.0% CCP-V-1  16.0% CCP-20CF₃ 7.0% CCP-30CF₃  8.0% DU-2-S  9.0% DU-3-S  10.0% CGZP-3-OT  3.0% BCH-32 4.0% CBC-33  1.0% Clearing point [° C.]: +69.5 Δn [589 nm; 20° C.]: +0.1006 Δε [1 kHz; 20° C.]:  +9.2 γ₁ [mPa · s; 20° C.]:  62 V₀ [20°C.]:  1.18 V

EXAMPLE 2

An IPS display contains a nematic mixture having CC-3-V  19.0% CC-3-V1 8.0% CCH-35  5.0% PDX-3  5.0% ME2N.F  4.0% CCP-V-1  16.0% CCP-20CF₃ 6.0% CCP-30CF₃  7.0% CCG-V-F  6.0% DU-2-S  9.0% DU-3-S  10.0% CGZP-3-OT 5.0% Clearing point [° C.]: +65.5 Δn [589 nm; 20° C.]:  +0.0965 Δε [1kHz; 20° C.]:  +9.7 γ₁ [mPa · s; 20° C.]:  59 V₀ [20° C.]:  1.18 V

EXAMPLE 3

An IPS display contains a nematic mixture having CC-3-V 19.0% CC-3-V19.0% CCH-35 5.0% PDX-3 5.0% ME2N.F 3.5% CCP-V-1 15.0% CCP-20CF₃ 7.5%CCP-30CF₃ 7.0% DU-2-S 10.0% DU-3-S 8.0% CGZP-2-OT 5.0% BCH-32 5.0%CBC-33 1.0%

EXAMPLE 4

An IPS display contains a nematic mixture having CC-3-V 19.0% CC-3-V18.0% CC-5-V 5.0% PDX-3 5.0% ME2N.F 4.0% CCP-V-1 16.0% CCP-20CF₃ 6.0%CCP-30CF₃ 7.0% CCG-V-F 6.0% DU-2-S 9.0% DU-3-S 10.0% CGZP-3-OT 5.0%

EXAMPLE 5

An IPS display contains a nematic mixture having CC-3-V 19.0% CC-3-V18.0% CCH-35 5.0% PDX-3 5.0% ME2N.F 4.0% CCP-V-1 16.0% CCP-20CF₃ 6.0%CCP-30CF₃ 7.0% DU-2-S 9.0% DU-3-S 10.0% CGZP-3-OT 5.0% BCH-32 6.0%

EXAMPLE 6

An IPS display contains a nematic mixture having CC-3-V1 9.0% CC-5-V9.0% CC-3-V 18.0% B-10.F0CF₃ 5.0% P-CF = CF-P-3-3 6.0% DU-2-S 15.0%PGU-2-F 7.0% BCH-32 6.0% CCP-V-1 15.0% BCH-2S.F.F 10.0% S → N [° C.]:<−40 Clearing point [° C.]: +65.0 Δn [589 nm; 20° C.]: +0.1288 Δε [1kHz; 20° C.]: +7.0 γ₁ [mPa · s; 20° C.]: 50

EXAMPLE 7

An IPS display contains a nematic mixture having CC-3-V 19.0% Δn [589nm; 20° C.]: +0.1013 CC-3-V1 9.0% Δε [1 kHz; 20° C.]: +8.7 CCH-35 5.0%γ₁ [mPa · s; 20° C.]: 64 CGZP-2-OT 5.5% V₀ [20° C.]: 1.16 V PDX-3 7.0%ME2N.F 2.0% CCZU-2-F 6.0% DU-2-S 10.0% DU-3-S 8.0% CCP-30CF₃ 6.0%CCP-V-1 15.0% BCH-32 6.0% CBC-33 1.5%

EXAMPLE 8

An IPS display contains a nematic mixture having CC-3-V 19.0% Clearingpoint [° C.]: +70.9 CC-3-V1 9.0% Δn [589 nm; 20° C.]: +0.0985 CC-5-V4.0% Δε [1 kHz; 20° C.]: +7.2 CCH-35 4.0% γ₁ [mPa · s; 20° C.]: 51PCH-301 2.0% PDX-3 2.0% K6 2.0% DU-2-S 10.0% DU-3-S 8.0% CCP-20CF₃ 8.0%CCP-30CF₃ 5.0% CGZP-2-OT 7.0% CCP-V-1 15.0% BCH-32 5.0%

EXAMPLE 9

An IPS display contains a nematic mixture having CC-3-V 19.5% Clearingpoint [° C.]: +72.3 CC-3-V1 9.0% Δn [589 nm; 20° C.]: +0.0997 CCH-355.0% Δε [1 kHz; 20° C.]: +9.1 PDX-3 6.5% γ₁ [mPa · s; 20° C.]: 56 ME2N.F3.5% CCP-V-1 15.0% CCP-20CF₃ 8.0% CCP-30CF₃ 7.0% DU-2-S 9.0% DU-3-S 8.0%CGZP-2-OT 3.5% BCH-32 5.0% CBC-33 1.0%

EXAMPLE 10

An IPS display contains a nematic mixture having CC-3-V1 10.0% Clearingpoint [° C.]: +69.9 CC-3-V 19.0% Δn [589 nm; 20° C.]: +0.1000 CC-5-V5.0% Δε [1 kHz; 20° C.]: +7.3 CCH-35 5.0% γ₁ [mPa · s; 20° C.]: 50PCH-301 2.0% DU-2-S 8.0% DU-3-S 8.0% PDX-3 3.0% K6 4.0% CGZP-2-OT 8.0%CCP-30CF₃ 8.0% BCH-32 5.0% CCP-V-1 15.0%

EXAMPLE 11

An IPS display contains a nematic mixture having CC-3-V1 28.0% Clearingpoint [° C.]: +79.8 CCH-35 5.0% Δn [589 nm; 20° C.]: +0.1056 PDX-3 5.0%Δε [1 kHz; 20° C.]: +9.7 ME2N.F 4.0% γ₁ [mPa · s; 20° C.]: 68 CCP-V-116.0% CCP-20CF₃ 7.0% CCP-30CF₃ 8.0% DU-2-S 19.0% CGZP-3-OT 3.0% BCH-324.0% CBC-33 1.0%

What is claimed is:
 1. An electro-optical liquid-crystal display havinga realignment layer for realignment of the liquid crystals whose fieldhas a component parallel to the liquid-crystal layer that is crucial forthe realignment, containing a liquid-crystalline medium of positivedielectric anisotropy, wherein said the medium comprises one or morecompounds of formula I

in which R¹ is an alkyl or alkenyl radical having up to 15 carbon atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, and L is H or F.
 2. A liquid-crystaldisplay according to claim 1, wherein said medium additionally comprisesat least one compound of formula II:

in which R² is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—,—O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, A¹ and A² are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6diyl and1,2,3,4-tetrahydronaphthalene-2,-diyl, where the radicals (a), (b) and(c) may be substituted by one or two fluorine atoms, Z¹ and Z² are each,independently of one another, —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CH₂CH₂—,—CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF₂— or a singlebond, and one or the radicals Z¹ and Z² is alternately —(CH₂)₄— or—CH═CH—CH₂CH₂—, L¹ and L2 are each, independently of one another, H orF, and m is 0, 1 or
 2. 3. A liquid-crystal display according to claim 1,wherein said medium additionally comprises at least one compound offormula III

in which R³ is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—,—O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, A³ and A⁴ are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo-[2.2.2]octylene,piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyland 1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a), (b)and (c) may be substituted by one or two fluorine atoms, Z³ and Z⁴ areeach, independently of one another, —CO—O—, —O—CO—, —CH₂O—, —OCH₂—,—CH₂CH₂—, —CH═CH—, —C≡C—, —CHF═CHF—, —CF—CF—, —CF₂O—, —OCF₂—, —CF₂CF₂—or a single bond, and one or the radicals Z³ and Z⁴ is alternatively—(CH₃)₄— or —CH═CH—CH₂CH₂—, and n is 0, 1 or
 2. 4. A liquid-crystaldisplay according to claim 1, wherein said medium additionally comprisesat least one compound of formula IV R⁴-(A⁵-Z⁵)₀-A⁶-R⁵  IV in which R⁴and R⁵ are each, independently of one another, H, an alkyl or alkenylradical having up to 15 carbon atoms which is unsubstituted,monosubstituted by CN or CF₃ or at least monosubstituted by halogen andin which, in addition, one or more CH₂ groups in these radicals may alsoeach, independently of one another, be replaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, A⁵ and A⁶ are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4,diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a), (b) and(c) may be substituted by one or two fluorine atoms, each Z⁵,independently, is —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CH₂CH₂—, —CH═CH—,—C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF₂— or a single bond,and one or the Z⁵ is alternatively —(CH₂)₄— or —CH═CH—CH₂CH₂—, and o is1, 2 or
 3. 5. A liquid-crystal display according to claim 1, whereinsaid medium additionally comprises at least one compound of formula V

in which R⁶ is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, A⁷ and A⁸ are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6diyl and1,2,3,4-tetrahydronaphthalene2,6-diyl, where the radicals (a), (b) and(c) maybe substituted by one or two fluorine atoms, Z⁷ and Z⁸ are each,independently of one another, —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CH₂CH₂—,—CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF₂— or a singlebond, and one or the radicals Z⁷ and Z⁸ is alternatively —(CH₂)₄— or—CH═CH—CH₂CH₂—, L¹ and L² are each, independently of one another, H orF, Q is a polyfluoroalkylene radical of the formula—(O)_(q)—(CH₂)_(r)(CF₂)_(s), —(O)_(q)—(CHF)_(r)(CF₂)_(s) or—(O)_(q)—(CF₂)_(r)(CHF)_(s)—CF₂—, in which q is 0 or 1, r is 0, 1, 2, 3,4, 5 or 6, s is 1, 2, 3, 4, 5 or 6, X is H, F or Cl and p is 0, 1 or 2.6. A liquid-crystal display according to claim 1, wherein said mediumadditionally comprises at least one compound of formula VI

in which R⁷ is an alkenyl group having 2 to 7 carbon atoms, Z⁹ is—CH═CH—, —CH₂CH₂— or a single bond, L is H or F, a is 0 or 1, and R⁸ isan alkyl, alkoxy or alkenyl group having up to 12 carbon atoms, inwhich, in addition, one or two non-adjacent CH₂ groups are eachoptionally replaced by —CO—, —OCO— or —COO—, or, if a is 1, R⁸ mayalternatively be F.
 7. A liquid-crystal display according to claim 1,wherein said medium additionally comprises at least one compound offormula II, at least one compound of formula III, or both

in which R² is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—,—O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, A¹ and A² are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a), (b) and(c) may be substituted by one or two fluorine atoms, Z¹ and Z² are each,independently of one another, —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CH₂CH₂—,—CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF₂— or a singlebond, and one or the radicals Z¹ and Z² is alternatively —(CH₂)₄— or—CH═CH—CH₂CH₂—, L¹ and L² are each, independently of one another, H orF, m is 0, 1 or 2, R³ has one of the meanings indicated for R², A³ andA⁴ each, independently of one another, have one of the meaningsindicated for A¹ and A², Z³ and Z⁴ each, independently of one another,have one of the meanings indicated for Z¹ and Z², and n is 0, 1 or
 2. 8.A liquid-crystal display according to claim 1, wherein pixels withinsaid display are addressed by means of an active matrix.
 9. Aliquid-crystalline medium of positive dielectric anisotropy comprisingtwo or more liquid-crystalline compounds wherein said medium contains atleast one compound according to formula I

in which R¹ is an alkyl or alkenyl radical having up to 15 carbon atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, and L is H or F.
 10. In a method ofgenerating an electro-optical effect using a liquid-crystal display, theimprovement wherein said display contains a liquid-crystalline mediumaccording to claim
 9. 11. A liquid-crystal display according to claim 7,wherein said medium comprises from 2 to 40% by wt. of at least onecompound of formula I, from 15 to 85% by wt. of at least one compoundselected from formulae II and/or III, from 0 to 60% by wt. of at leastone compound of formula IV R⁴-(A⁵-Z⁵)₀-A⁶-R⁵  IV in which R⁴ and R¹each, independently of one another, H, an alkyl or alkenyl radicalhaving up to 15 carbon atoms which is unsubstituted, monosubstituted byCN or CF₃ or at least monosubstituted by halogen and in which, inaddition, one or more CH₂ groups in these radicals may also each,independently of one another, be replaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O in such a way that O atoms are notlinked directly to one another, A⁵ and A⁶ are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a), (b) and(c) may be substituted by one or two fluorine atoms, each Z⁵,independently, is —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CH₂CH₂—, —CH═CH—,—C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF₂— or a single bond,and one or the Z⁵ is alternatively —(CH₂)₄ or —CH═CH—CH₂CH₂—, and o is1, 2 or 3 from 0 to 40% by wt. of at least one compound of formula V

in which R⁶ is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O in such a way that O atoms are notlinked directly to one another, A⁷ and A⁸ are each, independently of oneanother, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenyleneradical, in which, in addition, one or more non-adjacent CH₂ groups maybe replaced by —O— and/or —S—, (b) a 1,4-phenylene radical, in which, inaddition, one or two CH groups may be replaced by N, (c) a radical fromthe group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a), (b) and(c) may be substituted by one or two fluorine atoms, Z⁷ and Z⁸ are each,independently of one another, —CO—O—, —O—CO—, —CH₂O—OCH₂—, —CH₂CH₂—,—CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF— or a singlebond, and one or the radicals Z⁷ and Z⁸ is alternatively —(CH₂)₄— or—CH═CH—CH₂CH₂—, L¹ and L² are each, independently of one another, H orF, O is a polyfluoroalkylene radical of the formula—(O)_(q)—(CH₂)_(r)(CF₂)_(s), —(O)_(q)—(CHF)_(r)(CF₂)_(s) or—(O)_(q)—(CF₂)_(r)(CHF)_(s)—CF₂—, q is 0 or 1, r is 0, 1, 2, 3, 4, 5 or6, s is 1, 2, 3, 4, 5 or 6, X is H, F or Cl, and p is 0, 1 or 2, andfrom 0 to 55% by wt. of at least one compound formula VI

in which R⁷ is an alkenyl group having 2 to 7 carbon atoms, Z⁹ is—CH═CH—, —CH₂CH₂— or a single bond, L is H or F, a is 0 or 1, and R⁸ isan alkyl, alkoxy or alkenyl group having up to 12 carbon atoms, inwhich, in addition, one or two non-adjacent CH₂ groups are eachoptionally replaced by —CO—, —OCO— or —COO—, or, if a is 1, R⁸ mayalternatively be F.
 12. A display according to claim 1, wherein L is F.13. A display according to claim 1, wherein R¹ is alkyl or alkenylhaving up to 7 carbon atoms.
 14. A display according to claim 1, whereinR¹ is ethyl, n-propyl, n-pentyl, vinyl, 1E-alkenyl or 3E-alkenyl.
 15. Adisplay according to claim 1, wherein said liquid-crystalline mediumadditionally comprises one or more compounds of formula III′

in which R^(3′) is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, A^(3′) and A^(4′) are each,independently of one another, (a) a trans-1,4-cyclohexylene radical or1,4-cyclohexenylene radical, in which, in addition, one or morenon-adjacent CH₂ groups may be replaced by —O— and/or —S—, (b) a1,4-phenylene radical, in which, in addition, one or two CH groups maybe replaced by N, (c) a radical from the group consisting of1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a), (b) and(c) may be substituted by one or two fluorine atoms, Z^(3′) and Z^(4′)are each, independently of one another, —CO—O—, —O—CO—, —CH₂O—, —OCH₂—,—CH₂CH₂—, —CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF₂O—, —OCF₂—, —CF₂CF₂—or a single bond, and one or the radicals Z¹ and Z² is alternatively—(CH₂)₄— or —CH═CH—CH₂CH₂—, and n′ is 0, 1 or
 2. 16. A display accordingto claim 2, wherein the compounds of formula II are selected from thefollowing formulae:


17. A display according to claim 1, wherein said medium additionallycomprises one or more compounds selected from formulae VIIa to VIIc:

in which R⁹ is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another.
 18. A display according to claim 1,wherein said medium additionally comprises one or more compounds offormula VIII

in which R¹⁰ and R¹¹ are each, independently of one another,straight-chain alkyl or alkoxy.
 19. A display according to claim 1,wherein said medium additionally comprises one or more compounds offormula IX

in which R² is H, an alkyl or alkenyl radical having up to 15 carbonatoms which is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen and in which, in addition, one or more CH₂groups in these radicals may also each, independently of one another, bereplaced by —O—, —S—,

 —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another.
 20. A display according to claim 1,wherein said medium additionally comprises one or more compounds ofnegative dielectric anisotropy selected from formulae X, XI and XII:

in which R¹³ and R¹⁴ each, independently of one another, are H, an alkylor alkenyl radical having up to 15 carbon atoms which is unsubstituted,monosubstituted by CN or CF₃ or at least mono-substituted by halogen andin which, in addition, one or more CH₂ groups in these radicals may alsoeach, independently of one another, be replaced by —O—, —S—

 —CO—, —CO—O—, —O—CO— or —O—CO—O—, in such a way that O atoms are notlinked directly to one another.
 21. A display according to claim 1,wherein said medium additionally comprises one or more difluorostilbenesof formula XIII,

in which Alkyl* and Alkyl** are each independently a straight-chainalkyl radical having 1 to 6 carbon atoms.
 22. A display according toclaim 1, wherein said medium additionally comprises one or morecompounds of the formula XIV

in which R¹⁵ has one of the meaning defined for R¹, and L¹ and L² areeach, independently of one another, H or F.
 23. A display according toclaim 1, wherein said medium additionally comprises one or morecompounds of the formula XV

in which R¹⁶ has one of the meanings defined for R¹.
 24. A displayaccording to claim 1, wherein said medium contains from 2 to 40% byweight of at least one compound of formula I.
 25. A display according toclaim 7, wherein said medium contains from 15 to 85% by weight of atleast one compound selected from the compounds of formulae II and III.26. A display according to claim 4, wherein said medium contains up to60% by weight of at least one compound of the formula IV.
 27. A displayaccording to claim 5, wherein said medium contains up to 40% by weightof at least one compound of the formula V.
 28. A display according toclaim 6, wherein said medium contains up to 55% by weight of at leastone compound of the formula VI.
 29. A display according to claim 1,wherein said medium has a birefringence (Δn) of <0.14.
 30. A displayaccording to claim 1, wherein said medium has a bireflingence in therange from 0.06 to 0.13.
 31. A display according to claim 1, whereinsaid medium has a flow viscosity ν₂₀ (at 20° C.) of less than 30mm²·s⁻¹.
 32. A display according to claim 1, wherein said medium has aflow viscosity ν₂₀ (at 20° C.) of between 15 and 25 mm²·s⁻¹.
 33. Adisplay according to claim 1, wherein said medium has a specificresistance at 20° C. of from 5×10¹⁰ to 5×10¹⁴Ω·cm.
 34. A displayaccording to claim 1, wherein said medium has a rotational viscosity γ₁at 20° C. of less than 80 mPa·s.